Edge sealant confinement and halo reduction for optical devices

ABSTRACT

Techniques are described for using confinement structures and/or pattern gratings to reduce or prevent the wicking of sealant polymer (e.g., glue) into the optically active areas of a multi-layered optical assembly. A multi-layered optical structure may include multiple layers of substrate imprinted with waveguide grating patterns. The multiple layers may be secured using an edge adhesive, such as a resin, epoxy, glue, and so forth. A confinement structure such as an edge pattern may be imprinted along the edge of each layer to control and confine the capillary flow of the edge adhesive and prevent the edge adhesive from wicking into the functional waveguide grating patterns of the layers. Moreover, the edge adhesive may be carbon doped or otherwise blackened to reduce the reflection of light off the edge back into the interior of the layer, thus improving the optical function of the assembly.

CROSS-REFERENCE TO RELATED APPLICATION

The present disclosure is related to, and claims priority to, U.S.Provisional Patent Application Ser. No. 62/380,066, titled “Edge SealantConfinement and Halo Reduction for Optical Devices,” which was filed onAug. 26, 2016, the entirety of which is incorporated by reference intothe present disclosure.

BACKGROUND

Jet and Flash Imprint Technology (J-FIL™), developed by MolecularImprints™ provides the ability to pattern various three-dimensionalnano-structures on a surface using a mold that is formed withnano-structures. Ultraviolet (UV) curable liquid photoresist is flowedthrough the mold and cured with light. The mold is then separated fromthe cured photoresist, leaving behind shapes on a surface. An eyepiecemay be composed of multiple layers of glass, and the J-FIL technique maybe used to create diffraction gratings on the various layers of theglass. The layers may be stacked and glue may be employed to providemechanical integrity and seal the assembly, with air gaps between thelayers for optical performance. Traditionally in such assemblies, theglue may wick (e.g., flow) from the edges into the functional areas ofthe assembly, leading to optical degradation.

SUMMARY

Embodiments of the present disclosure are generally directed to anoptical structure and/or optical device that includes multiple layers.More specifically, embodiments are directed to a multi-layer opticalstructure in which an edge pattern is imprinted on at least some of thelayers to inhibit or prevent, and otherwise control, the flow of an edgeadhesive into a grating pattern that is imprinted onto the variouslayers.

In general, innovative aspects of the subject matter described in thisspecification can be embodied as a structure (e.g., an opticalstructure) that includes a substrate including an edge grating patternthat is proximal to an edge of the substrate, the edge grating patternincluding one or more features arranged to control capillary flow of amaterial from the edge of the substrate into the edge grating pattern.

Embodiments can optionally include one or more of the followingfeatures.

In some embodiments, the edge grating pattern is on a first surface ofthe substrate, and the substrate further includes a second gratingpattern on a second surface of the substrate.

In some embodiments, the second grating pattern is a functional gratingpattern that includes one or more of an orthogonal pupil expander (OPE)region and an exit pupil expander (EPE) region.

In some embodiments, the one or more features are arranged to besubstantially perpendicular to the edge of the substrate.

In some embodiments, the one or more features include one or more of aV-shaped grating pattern, an S-shaped grating pattern, and a rectangulargrating pattern.

In some embodiments, the edge grating pattern further includes one ormore second features arranged to inhibit the capillary flow of thematerial beyond the edge grating pattern.

In some embodiments the one or more second features are arranged to besubstantially parallel to the edge of the substrate.

In some embodiments, the one or more second features differ, at least inpart, from the one or more features in at least one of depth, height,and width.

In some embodiments, the material has a refractive index that is lowerthan that of the substrate.

In some embodiments, the material, as applied, has a gradient ofrefractive index that varies according to a distance from the edge ofthe substrate.

In some embodiments, the one or more features have a cross-sectionalshape of at least one polygon.

In some embodiments, the at least one polygon includes one or more of atriangle, a square, and a rectangle.

In some embodiments, the substrate is a waveguide configured to receiveand propagate light; and the material is a light variable absorptiveedge material configured to receive and absorb light from the waveguide.

In some embodiments, the material and the substrate have a substantiallysame index of refraction.

In some embodiments, the material comprises a doping agent and anadhesive.

In some embodiments, the doping agent is distributed at a gradient thatvaries with distance from an edge of the waveguide.

In some embodiments, the doping agent comprises carbon blacknanoparticles.

In some embodiments, the carbon black nanoparticles have a diameter in arange of 50-70 nm.

In some embodiments, the material comprises at least one layer ofadhesive tape.

In some embodiments, the adhesive tape comprises a doping agent and anadhesive.

In some embodiments, the adhesive tape and the substrate have asubstantially same index of refraction.

In some embodiments, the substrate is one of a plurality of layers ofsubstrate included in the optical structure, each of the plurality oflayers includes the edge grating pattern proximal to a respective edgeof the layer, and the material is an edge adhesive that is applied alongat least a portion of a perimeter of the optical structure to secure theplurality of layers of substrate.

In some embodiments, each of the plurality of layers of substratefurther includes a second grating pattern.

In some embodiments, the edge grating pattern is arranged to provide fora capillary flow of the edge adhesive into the edge grating pattern, andis further arranged to inhibit the capillary flow of the edge adhesiveinto the second grating pattern.

In some embodiments, the second grating pattern is of a nano-scale andoperate as a waveguide for light propagation; and the edge gratingpattern is one or more of a micro-scale and a nano-scale.

It is appreciated that aspects and features in accordance with thepresent disclosure can include any combination of the aspects andfeatures described herein. That is, aspects and features in accordancewith the present disclosure are not limited to the combinations ofaspects and features specifically described herein, but also include anycombination of the aspects and features provided.

The details of one or more embodiments of the present disclosure are setforth in the accompanying drawings and the description below. Otherfeatures and advantages of the present disclosure will be apparent fromthe description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1D depict an example eyepiece according to the prior art, theeyepiece exhibiting wicking of edge material into the gaps betweenlayers.

FIGS. 2A-2D depict an example eyepiece including an edge pattern toconfine edge material, according to some embodiments of the presentdisclosure.

FIG. 3A depicts examples of substantially linear edge patterns that maybe employed to prevent wicking of edge material, according to someembodiments of the present disclosure.

FIG. 3B depicts examples of pillar edge patterns that may be employed toprevent wicking of edge material, according to some embodiments of thepresent disclosure.

FIG. 4A depicts a cross-sectional view of an example eyepiece includingmultiple layers, according to some embodiments of the presentdisclosure.

FIG. 4B depicts a cross-sectional view of an example eyepiece accordingto the prior art, the eyepiece exhibiting wicking of edge material intothe gaps between layers.

FIG. 4C depicts a cross-sectional view of an example eyepiece includingan edge pattern to confine edge material, according to some embodimentsof the present disclosure.

FIG. 5A depicts an example layer of an eyepiece, according to someembodiments of the present disclosure.

FIG. 5B depicts an example virtual reality and/or augmented realitysystem that employs a multi-layered eyepiece, according to someembodiments of the present disclosure.

FIGS. 6A and 6B depict example test images in an eyepiece withunblackened and blackened edges respectively, according to someembodiments of the present disclosure.

FIG. 7 depicts an example of a progressive gradient edge sealant bysuccessive layers, according to some embodiments of the presentdisclosure.

FIG. 8 depicts an example of a progressive gradient edge sealant byvarying grating pitch, according to some embodiments of the presentdisclosure.

FIG. 9 depicts a cross-sectional view of an example eyepiece including acombination of light mitigation material and adhesive material,according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed to using confinementstructures and/or pattern gratings to reduce or prevent the wicking ofsealant polymer (e.g., glue) into the optically active areas of amulti-layered optical assembly. Embodiments are further directed toimproving adhesion between layers of an optical assembly, thus improvingthe structural integrity. Embodiments are further described to utilize aprogressively doped sealant material to reduce reflective instanceswithin the optical assembly, or halo effects, thus improving the opticalfunction of an eyepiece or other multi-layer diffraction gratingassembly.

An eyepiece may be composed of multiple layers of (e.g., high index)glass in a stack. The J-FIL technique may be used to create diffractiongratings on the layers of the glass of the eyepiece to create waveguidedisplays. Each layer may be a thin layer of glass with polymer gratingscreated on its surface using J-FIL. The diffraction gratings may providethe basic working functionality of the eyepiece. Once the diffractiongratings are formed onto a large, broad glass layer, the glass layer maybe laser cut into the shape of the eyepiece. Each layer of glass may bea different color, and there may be multiple depth planes. A largernumber of planes may provide for a better virtual experience for a userusing the eyepiece. The layers may be stacked using the sealant polymer(e.g., glue dots), and the whole stack may be sealed using the sealant.Air gaps between the layers may be needed for the optical performance ofthe eyepiece. The gaps between the layers may have controlled dimensions(e.g., substantially uniform width). The edge sealant polymer (alsodescribed herein as glue) may be applied around the edge of the layeredstructure to seal the stack and air gaps from the outside environment.The edge seal glue also provides a physical lock to ensure mechanicalintegrity of the structure, while keeping out contamination andmoisture. Without such a seal, the layers may fall apart and delaminatefrom one another. However, because edge seal glue is liquid, it may wick(e.g., flow) into the gaps between the layers, into the functional area(e.g., diffraction gratings) of the structure, and degrade the opticalperformance of the eyepiece.

In some embodiments, the polymer is in contact with both layers of thewaveguide stack. Such dual contact is especially critical for thoseembodiments that employ an ultraviolet (UV) acrylate-based polymercuring material. In these embodiments, the contact with both the layerabove and below the wicked polymer ensure ensures proper UV cure andlimits oxygen inhibition. Uncured or undercured polymer producesundesirable characteristics such as poor adhesion to glass, inferiormechanical properties, lower glass transition temperature, and/orothers. FIG. 4B illustrates wicking with poor contact between the layersof the waveguide stack. FIG. 4C illustrates proper contact, asfacilitated by edge confinement structures as described throughout thisdisclosure.

Some embodiments provide additional features, edge confinementstructures, that are imprinted onto the glass. Such edge confinementstructures may have different shapes (e.g., gratings, pillars, polygons,honeycomb hexagonal lines, etc.) and/or heights compared to those of thenon-edge diffraction gratings in the interior of the structure. The edgeconfinement structures may be inset from the edge of the glass layers,and may act as a dam to prevent the edge seal glue from wicking into theinterior of the eyepiece, into the area of the functional non-edgediffraction gratings. J-FIL may be used to create both the functionalregion of the optics, e.g., non-edge diffraction gratings, and the edgeconfinement features for mechanical packaging of the device to preventwicking of the edge seal glue into the functional region.

In some embodiments, using the J-FIL drop-on-demand process, UV curablematerial that forms a confinement region along the perimeter of adiffraction grating eyepiece is co-imprinted with optically functionaldiffraction gratings. The combination of the optically activediffraction gratings with the confinement structures may be efficientlyachieved by incorporating the confinement structures into the patternedmaster that is utilized as the original source for the eyepiecediffraction gratings. Upon replication steps from the master tosubmaster, and then to the substrate, these confinement structures maybe imprinted during the same process in which the diffraction gratingsare imprinted. In some embodiments, the confinement structures arearranged along the perimeter of the eyepiece such that after a largersubstrate is patterned using J-FIL, and subsequently singulated (e.g.,laser cut) into the shape of the eyepiece, these confinement structuresrun parallel (or substantially parallel) and/or adjacent to thesingulated edge. The confinement structures may be arranged to reduceand/or restrict the lateral flow of edge sealant polymer (e.g., thebonding glue dots) from the edge of the eyepiece stack (e.g., themulti-layer diffraction grating eyepiece) towards the functionalnon-edge eyepiece gratings. Such flow would occur otherwise throughnatural capillary action, with a narrower gap between layers providingfor a string capillary action pull of the glue into the interior of thestructure. Further, as described above in relation to FIG. 4C, suchconfinement structures may further improve polymer contact betweenlayers to improve curing and structural integrity.

Such confinement structures may resist the flow of the low viscosityphotoresist in the J-FIL process, but have not been previously been usedto prevent wicking of polymer sealant. Moreover, the confinementstructures described herein may be imprinted and/or structureddifferently compared to the structures that are used to resist the flowof the low viscosity photoresist in the J-FIL process. In particular,structures that are used to merely resist the flow of the photoresistmay be inadequate to prevent the capillary action wicking of thesealant. For example, a grid layout has been previously used to resistthe flow of photoresist, whereas the embodiments of confinementstructures as disclosed herein may include a set of parallel ridgesrunning along the perimeter to block the capillary flow of the sealant.In general, previously used structures may have been designed to controlthe flow of photoresist through a particular structure formation,whereas embodiments disclosed herein provide confinement structures thatare arranged to prevent the flow of sealant altogether, redirect theflow of the sealant along perimeter to prevent wicking into the interiorof the structure, and/or improve manufacturing and structural metrics.In some embodiments, the sealant may have a higher viscosity than thephotoresist. The sealant may be applied (e.g., coated) along the edge ofthe stacked layers of the eyepiece, instead of being dispensed asdiscrete droplets such as the photoresist dispensed in a J-FIL process.

In some embodiments, a confinement structure may include ananoimprinted, cured set of parallel lines that runs parallel (orsubstantially parallel) to the edge of the eyepiece. As the edge sealbegins to permeate the gap between eyepieces layers, capillary forcedraws the edge seal polymer along the perimeter rather than into theinterior of the eyepiece stack. The use of the sealant enables creationof high contrast eyepieces by absorbing stray light that hits the edgesof the eyepiece layers, as described later in this disclosure. Thesealant also provides structural integrity for (e.g., “locks in”) themechanical gap and co-planarity of the eyepieces. Without the use ofconfinement structures as described herein, the pooled sealant couldhave adverse properties by eventually contacting the eyepiecediffraction gratings that are inside the gap between two layeredsubstrates of the eyepiece. Upon contacting these, the capillary forcewould draw the sealant resin or glue into the diffraction grating, thusdegrading the optical function of the eyepiece by at least partlyfilling the diffraction gratings.

Moreover, in some embodiments, the capillary force that would draw thesealant along the perimeter may be enhanced by the nanostructure of theconfinement structures. For example, the confinement structure mayprevent wicking of sealant into the interior of the eyepiece while alsofacilitating the propagation of the sealant along the edge of theeyepiece. Because the capillary force may aid the distribution of thesealant along the edge, a sealant extruder or other sealant deliverydevice may not be needed to apply sealant along the entire circumferenceof an eye piece. Instead, a sealant delivery device may apply sealant toone or more locations along the circumference. The confinementstructures that include nanostructured line(s) that are parallel to theedge of the eyepiece may, through capillary action, distribute thesealant evenly to the remainder of the circumference. Thus, theconfinement structures may also enable the use of a simpler, lower cost,mechanism for applying sealant to the edge of the eyepiece.

Although examples herein describe the use of an edge pattern to divertor otherwise control the wicking flow of an adhesive and/orlight-absorptive edge material into the interior of the eyepiece,embodiments are not so limited. The techniques described herein can alsobe used to control the flow of a material that may not be adhesiveand/or light-absorptive. Additionally, while many embodiments describedhave edge patterns on the same side of a waveguide as diffractivegratings in a functional area of an eyepiece, it is possible for theedge patterns and diffractive gratings to be fabricated on oppositesides of a waveguide. In some embodiments, one or more of the edgepatterns and diffractive gratings may be disposed on one or more sidesof a waveguide substrate.

FIGS. 1A-1D depict an example eyepiece 100 according to the prior art,the eyepiece exhibiting wicking of edge material into the gaps betweenlayers. As described above, the eyepiece may have any suitable number oflayers of glass or other material, and each layer may act as a waveguideto allow the passage of various frequencies of light. Layers may beconfigured for particular wavelengths, so as to propagate light of aparticular color, and the eyepiece may be configured for a particularoptical power, to create a number of depth planes at which light throughthe waveguide may be perceived. For example, a first set of waveguidelayers may include layers for red, green, and blue at a first depthplane, and a second set of waveguide layers may include a second set oflayers for red, green, and blue light corresponding to a second depthplane. The order of the colors may be arranged differently in differentdepth planes to achieve the desired optical effects in the eyepiece. Insome embodiments, a single (e.g., blue) layer may cover multiple depthplanes.

A substrate 104 may be imprinted with a grating pattern 106, using theJ-FIL method or other suitable technique. In the examples of FIGS. 1Aand 1B, a portion of the substrate 104 has been imprinted with thepattern 106. In the examples of FIGS. 1C and 1D, the entire surface ofthe substrate 104 has been imprinted with a pattern 106. In general, anysuitable distance may separate the edge of the substrate 104 and thebeginning of the imprinted grating pattern 106.

As shown in the examples of FIGS. 1B and 1D, an edge material 108 hasbeen applied along the edge of the eyepiece. The edge material 108 maybe a glue, resin, polymer sealant, ink, and/or other viscous material.As illustrated, and as commonly occurs in the prior art, some of theedge material 108 has flowed into the interior of the eyepiece, awayfrom the edges, as wicking edge material 110. As described above, suchwicking may be caused by capillary action that draws the edge material108 into the gaps between layers in the eyepiece. Such wicking maydegrade the optical function of the eyepiece.

FIGS. 2A-2D depict an example eyepiece 200 including an edge pattern toconfine edge material, according to some embodiments of the presentdisclosure. As in the examples of FIGS. 1A-1D, a substrate 104 has beenimprinted with a grating pattern 106, using the J-FIL method or othersuitable technique. In the examples of FIGS. 2A and 2B, a portion of thesubstrate 104 has been imprinted with the pattern 106. In the examplesof FIGS. 2C and 2D, a greater portion of the surface of the substrate104 has been imprinted with a pattern 106.

In the examples of FIGS. 2A-2D, an edge pattern 202 has been appliedalong the edge of the eyepiece 200. In some instances, each layer of theeyepiece may have the edge pattern 202 applied. Alternatively, a subsetof the layers may have the edge pattern applied. Possible edge patternsare described further with reference to FIGS. 3A and 3B. In someinstances, as in FIGS. 2C and 2D, the edge pattern 202 may extend up tothe beginning of the grating pattern 106. In some instances, as in FIGS.2A and 2B, there may be some space between the edge pattern 202 and thegrating pattern 106. As shown in FIGS. 2B and 2D, the flow of the edgematerial 108 may be confined to the edge pattern 202, as confined edgematerial 204, at least partly (or entirely) preventing the edge materialfrom reaching the grating pattern 106 and thus degrading thefunctionality of the optically active portion of the layers.

In some instances, the gap between layers of the eyepiece may be on theorder of tens of microns (e.g., a 30 micron gap). The width of theapplied edge material may be on the order of millimeters. The gratingpatterns for the pattern 106 and/or edge pattern 202 may be on a smallerscale, e.g., nano-scale gratings. Given the small scale of thenano-scale gratings, such gratings may exhibit a very strong capillaryaction to draw the edge material 108 into the grating pattern 106. Toprevent the edge material 108 from wicking too far into the interior ofeach layer, and thus degrading the optical performance of the layers byfilling in the grating pattern 106, the edge pattern 202 may extend fromthe edge of each layer into the interior a distance on the order ofmillimeters. The edge pattern 202 may allow the edge material 108 toeffectively exhaust its capillary action in the “dummy” pattern ofconfinement structures, such that the edge material 108 is preventedfrom flowing into the grating pattern 106. In some embodiments, edgepattern 202 extends ten microns into the eyepiece. Alternatively, theedge pattern 202 can extend further, e.g., as far as five millimeters.Ancillary considerations such as adhesive properties desired, the typeof polymer used for sealant material, and/or the amount of lightabsorption desired can determine the amount of sealant utilized and thusthe depth of the edge pattern to be used.

In some embodiments, the edge pattern 202 may be applied in a same stepor same pattern application process as the grating pattern 106, e.g.,using J-FIL. The edge pattern 202 may be co-patterned along with thegrating pattern 106 in the same patterning process. Alternatively, theedge pattern 202 may be applied in a separate process, before or afterthe application of the grating pattern 106. The J-FIL applicationprocess can spatially control the volume density of the photoresist thatis applied to a substrate. A master pattern that is applied using J-FILmay be a mixture of different sized features. For example, nano-scalegratings may be used for the eyepiece grating pattern 106, whereas adeeper micro-scale or nano-scale grating may be used for the edgepattern 202 that controls the flow of the edge material 108. Thepatterning may be performed at the same time and/or during the sameapplication process, and more (e.g., a thicker layer of) photoresist maybe deposited to the areas that are to have the deeper features for edgecontrol compared to a thinner depositing of photoresist in the areasthat are to have the nano-scale patterning, such as the opticallyfunctional grating pattern 106 region of the eyepiece. In someinstances, optimal function of the eyepiece may require a very thinresidual layer of unpatterned photoresist under the nano-scale grating106, between the waveguide surface and the grating. Use of J-FIL fordepositing different thickness layers of photoresist provides anadvantage over traditional techniques, given that the area of thegrating pattern 106 requires a thin layer (e.g., as thin as feasible) ofphotoresist to be deposited, whereas the area of the edge pattern 202requires a much thicker layer of photoresist to support the edge patternthat is more deeply etched, e.g., micro-scale compared to nano-scaleetching of the grating pattern 106. As used herein, nano-scale refers toa distance scale on the order of (e.g., one to hundreds of)nanometer(s), whereas micro-scale refers to a distance scale on theorder of one to hundreds of micron(s), and millimeter-scale refers todistance scale on the order of one to hundreds of millimeters.

Although the examples herein include a particular pattern (e.g.,vertical lines), embodiments are not limited this example. Any suitablepattern may be imprinted to achieve desired optical functionality in theeyepiece. Moreover, although the example eyepieces herein may have aparticular shape (e.g., that of a lens in eyeglasses), the eyepiece mayhave any suitable shape.

FIG. 3A depicts example edge patterns 202 that may be employed toprevent wicking of edge material, according to some embodiments of thepresent disclosure. As illustrated in FIG. 3A, the edge of the eyepieceis located to the left of each of the examples 202(1)-202(4), such thatthe right side of each example of toward the interior of the eyepiece,e.g., toward the grating pattern 106. As shown in the examples 202(1)through 202(4), the edge pattern 202 may include two type of features.First feature(s) 302 may include one or more etched lines that runparallel (or approximately parallel) to the edge. Such feature(s) mayblock the edge material 108 (e.g., glue, resin, sealant, etc.) frompenetrating to the grating pattern 106. The feature(s) 302 may alsoredirect the edge material 108 to flow parallel to the edge instead ofperpendicular to the edge, e.g., inward toward the grating pattern 106.Second feature(s) 304 may include lines that run perpendicular, orsubstantially perpendicular, to the edge, to allow the edge material 108to flow inward for some distance from the edge before being blocked bythe first (e.g., parallel) features 302. In some embodiments, the edgepattern may include second feature(s) 304 such as a set of lines runningperpendicular (or approximately perpendicular) to the edge, as inexamples 202(1), 202(3), and 202(4). In some embodiments, the edgepattern may include second feature(s) 304 that guide the edge material108 along a more complex path, such as the V-shaped or chevron shapedpattern of example 202(2). Some embodiments support the use of anysuitable pattern for the edge pattern 202. For example, the pattern 202may include second feature(s) such as serpentine or S-shaped curvesinstead of the V-shaped chevron pattern of example 202(2). The use of aV-shaped, S-shaped, or other type of pattern may function to graduallyslow down the viscous flow of the edge material 108 as it progressesalong the patterned channels.

The second feature(s) 304 may function to pull the edge material 108inward in a controlled manner until the edge material 108 runs upagainst the first feature(s) 302, which act as a dam or block to preventthe edge material 108 from penetrating any further into the interior.The second features 304 may also facilitate the balanced distribution ofthe edge material 108 along the circumference of the edge. In someembodiments, the first features 302 may have a different width dimensioncompared to the second features 304. For example, as shown in examples202(2) through 202(4), the first features 302 may include wider etchedchannels compared to the second features 304. The second features 304may also have different heights compared to the first features 302. Forexample, the first features 302 may extend higher, or be etched deeper,than the second features 304. The different dimensions, e.g., height,depth, and/or width, of the first feature(s) 302 may provide a moreeffective dam or block to inhibit the flow of the edge material 108.

Although FIG. 3A shows various examples of edge patterns 202 that may beemployed, embodiments are not limited to the examples shown. Someembodiments may employ edge patterns 202 of any suitable design, size,or other arrangement to confine the flow of the edge material 108 awayfrom the functional portion of the eyepiece. In some instances, theparticular depth, width, and/or design of the edge pattern 202 may bebased at least partly on the viscosity or other characteristics of theedge material 108. For example, a first edge pattern 202 may optimallyconfine an edge material 108 of a particular viscosity whereas a second,different edge pattern 202 may optimally confine a different edgematerial 108 having a different viscosity.

FIG. 3B depicts example grating patterns as pillar structures 202(5)through 202(10) that may be utilized to yield results similar to thoseresulting from use of example patterns 202(1) through 202(4). Eachpillar grating pattern may have, in addition to a cross-sectionalgeometry, a height extending in a z direction from a surface of asubstrate. The plurality of spaced-apart pillars, in addition to havingvariable geometries, may have variable sizes as well.

As depicted in FIG. 3B, the example triangle pillars 202(5), which mayhave variable height in a z-direction among the depicted pillars, have acommon size and geometry, while the example triangular pillars 202(6)may have variable size among the various pillars to control the rate ofwicking by capillary action as a function of variable pitch volumebetween the pillars across the pattern. Other shapes and combinations,such as circular pattern 202(7), hexagonal pattern 202(8), and/or squarepattern 202(9), may achieve similar function. Additionally, someembodiments may utilize combinations, such as circular pillars nearerthe edge and triangular pillars nearer a functional area, or such asexample pattern 202(10) with square pillars to facilitate wicking intothe pattern and linear gratings to provide a flow control in desiredorientations. In some embodiments, linear gratings as shown in examplepattern 202(10) may be substantially parallel with one or more edges ofa waveguide. Embodiments may also employ other suitable patterns,including any suitable modifications or derivations from the exampleconfigurations shown in FIGS. 3A and 3B.

FIG. 4A depicts a cross-sectional view of an example eyepiece 200including multiple layers, according to some embodiments of the presentdisclosure. As shown in the example of FIG. 4A, the eyepiece 200 mayinclude any appropriate number of layers 404 which are separated fromone another by a gap. The gap between layers 404 may be of any suitablewidth to achieve the desired optical functionality. Each layer 404 mayinclude a substrate, a grating pattern 106 in the optically functionalregion of the eyepiece, and an edge confinement area that has beenetched with an edge pattern to inhibit or prevent the flow of edgematerial into the grating pattern 106.

FIG. 4B depicts a cross-sectional view of an example eyepiece 100according to the prior art, the eyepiece exhibiting wicking of edgematerial into the gaps between layers. As shown in this cross-sectionalview, the edge material is flowing through the gaps between layerstoward the functional region that includes the grating pattern 106. Asdescribed above, the impinging of the edge material 108 into the gratingpattern 106 may degrade or effectively destroy the functionality of theeyepiece.

FIG. 4C depicts a cross-sectional view of an example eyepiece 200including an edge pattern 202 to confine the edge material 108 from thegrating pattern 106, according to some embodiments of the presentdisclosure. As shown in the example of FIG. 4C, the edge pattern 202includes two sets of features 302 and 304 having different heightsand/or depths. The presence of the edge pattern 202 has effectivelyconfined the edge material 108, preventing it from reaching the gratingpattern 106 through capillary action, and improving the adhesion andcuring properties of the edge material 108 during manufacture.

In some embodiments, as shown in the example of FIG. 4C, there may begap 402 between the edge pattern 202 and the grating pattern 106. Thisgap 402 should not be confused with the gap(s) between layers 404 of theeyepiece. In some embodiments, the gap 402 may have a width that is onthe order of tens of microns. In some embodiments, the gap 402 may havea different width at different positions along the eyepiece. Forexample, the gap 402 may have a different width near the nose comparedto near the temple, as the eyepiece is being worn by an individual. Thewidth of the gap 402 may be a function of the optics, e.g., according tothe desired optical properties at particular positions along thecircumference of the edge. In some embodiments, an edge pattern 202 maybe imprinted on both sides of layer 404.

FIG. 5A depicts an example layer 404 of an eyepiece 200, according toembodiments of the present disclosure. In the example of FIG. 5A, alayer is depicted having a rectangular shape. Some embodiments may alsoemploy layers of different shapes, such as the eyepiece shapes shown inthe previous figures. FIG. 5A shows a top-down view of a layer, in whichthe X- and Y-directions are along the surface of the layer and theZ-direction is orthogonal to the surface of the layer.

As shown in FIG. 5A, a layer may include one or more incoupling gratings(ICGs) 504 where light may be introduced into the layer. In the exampleof FIG. 5A, the ICG 504 is shown as three dots. Additional embodimentssupport other suitable arrangements for the ICG. Light 506 may propagatealong the X-direction from the ICG 504 toward the left edge of thelayer, according to the waveguides created in the layer by the gratingpattern 106. Light may also propagate along the X-direction toward theright edge of the layer. In some embodiments, the waveguides may bearranged to send more light preferentially in one direction, e.g., moretoward the left than toward the right.

For example, the layer may include a blackened edge 502(2) and ablackened edge 502(1). If the edge(s) are not blackened, the propagatinglight 506 may reflect back off the edge toward the interior of thelayer. Such reflection may cause undesirable “ghost” images in theeyepiece, e.g., when the eyepiece is used as a component in a wearablevirtual reality and/or augmented reality device. Accordingly, edgeblackening may prevent and/or reduce the intensity of ghost images. Insome embodiments, the edge along the right-hand and/or lower side of thelayer may also be blackened to prevent the occurrence of ghost imagesdue to light reflecting off the respective edges. In other words, theentire periphery of the eyepiece (or at least a substantial portionthereof) is blackened in some embodiments. Embodiments may provide anysuitable variations on selection of where to apply blackening to aparticular location.

In some embodiments, the layer may include at least two differentregions—an orthogonal pupil expander (OPE) region 508 and an exit pupilexpander (EPE) region 510. As light 506 is propagating along theX-direction in the OPE region, at least some of the light is diffractedby grating patterns in the Y-direction towards and into the EPE region510. In embodiments where the eyepiece is employed in a virtual realityand/or augmented reality device, the light is outcoupled from the EPEregion 510 to the eye(s) of user where it is perceived as a virtualimage. As discussed above, the top edge 502(1) may also be blackened toreduce or prevent the reflection of light that is propagating in theY-direction, given that such reflected light may produce undesirableoptical effects.

FIG. 5B depicts an example virtual reality and/or augmented realitysystem 500 that employs a multi-layered eyepiece, according toembodiments of the present disclosure. As shown in the example of FIG.5B, the system 500 may include a light emitting diode (LED) light source514 that directs light onto a reflective collimator 512. The collimator512 sends the collimated light to a liquid crystal on silicon (LCOS) SLM518, which may direct a light signal via a projector relay 516 to ICG504. The light signal may provide the virtual reality and/or augmentedreality image(s) to be shown to the user through the system 500. Asdescribed above, the eyepiece may include any suitable number of layers404 of imprinted substrates, and the eyepiece may include an OPE region508 and an EPE region 510. The light directed into the OPE region maypropagate across the OPE region and into the EPE region where itoutcouples the light to the viewer's eye 520 and is perceived as thevirtual and/or augmented reality image.

Blackening an edge of the multi-layer eyepiece may cause the absorptionof light impinging on the edge, and/or provide for reduced reflection oflight impinging on the edge. For example, in previously availabledevices the light reflected from an edge of the eyepiece may outcoupleto the viewer's eye 520 and, because of the longer path of the reflectedlight to viewer's eye 520, there may be undesirable phase changes of thereflected light relative to the intended original light path and anyimage embodied by the light will appear distorted by the resulting phaseinterference. In other cases, the reflected light may propagate througheyepiece layers 404 completely and appear on LCOS SLM 518 again where itwill be re-directed through the system as a “ghost” image. Such effectsare reduced or eliminated using the edge blackening provided by variousembodiments.

Various embodiments discussed herein support the use of any suitableprocess to blacken the edges of the eyepiece. For example, an epoxy suchas Masterbond EP42HT-2 with a refractive index n≈1.6 may be mixed in a2:1 ratio with carbon black. The blackened epoxy may be the edgematerial 108 that is employed to seal the eyepiece and providemechanical integrity for the multi-layer arrangement as described above.Other suitable types of light-absorbing material may also be employed.Although examples herein describe the use of a carbon black-doped epoxyas the edge material 108, embodiments are not so limited. The edgesealant may be any suitable material, and may be light absorbing throughthe doping of a glue, resin, epoxy, or other adhesive with blackchromate, carbon black, and/or other light absorbing substances.

FIGS. 6A and 6B depict example test images in an eyepiece withunblackened and blackened edges respectively, according to embodimentsof the present disclosure. These figures illustrate the optical effectof the edge blackening described with reference to FIG. 5A. Without theblackened edge(s), the test images exhibit lower contrast and lesssharpness compared to when the edge(s) are blackened.

Table 1 shows measurements of ANSI contrast and sequential contrast forthree experimental trials using an eyepiece without edge blackeningtreatment. Table 2 shows a similar measurement (for a singleexperimental trial) using an eyepiece with edge blackening treatment.

TABLE 1 Mean Standard deviation Standard error ANSI White 38.15 1.453.8% ANSI Black 8.03 4.75 2.4% ANSI Contrast 4.75 0.12 2.4% Full White47.00 2.43 5.2% Full Black 0.259 0.011 4.2% Sequential Contrast 181.31.8 1.0%

TABLE 2 Single trial ANSI White 19.27 ANSI Black 0.525 ANSI Contrast36.7 Full White 19.994 Full Black 0.1124 Sequential Contrast 177.9

As shown in Tables 1 and 2, the ANSI contrast is substantially improved(e.g., 36.7 vs. 4.75) with blackened edge(s), whereas the sequentialcontrast is similar (e.g., 181.3 vs. 177.9). Sequential contrast ismeasured by comparing an off image to an on image, e.g., contrast overtime as the image is switched on and off. ANSI contrast is the contrastbetween black and white for a particular image at a particular time. Theblackening of edge(s) may also reduce the occurrence and/or prominenceof halo effects that may occur in the eyepiece without blackening, suchhalo effects caused by reflection of light off of the edge(s).

Table 3 lists the results of absorption tests using different types ofadhesives as the edge material 108, in particular carbon black-dopedNorland 81 (with n=1.56), carbon black-doped Masterbond with n≈1.6, andSapphire (@ 523 nm) with n=1.77, e.g., a refractive index thatapproximately corresponds to the refractive index of the substrate usedin the layers of the eyepiece.

TABLE 3 Refractive Reflected Percentage Adhesive Index Power (W)Absorbed Sapphire (@ 523 nm) 1.77  1.42 mW   0% Norland 81 1.56 56.2 μW 96% Masterbond EP42HT-2 ≈1.6 59.1 μW 95.9%

As shown in Table 1, use of a blackened adhesive (e.g., edge material108) with a lower refractive index provides for a reduction of reflectedpower (e.g., of light reflecting off edges) of approximately two ordersof magnitude, from milliwatts to tens of microwatts, and a highpercentage of light absorbed at the edges. The percentage absorbed ascalculated as 100−100*the reflected power of the adhesive/the reflectedpower of the Sapphire adhesive (e.g., used as a baseline comparison).

In some embodiments, an edge adhesive may be utilized that facilitatesoptical performance. In some embodiments, the edge adhesive may beabsorptive to prevent reflection of light back through the eyepiece. Insome embodiments, the edge adhesive exhibits a refractive indexsubstantially similar to that of the eyepiece, as well as increasingconcentrations of absorptive material as a function of distance from theedge to permit light to propagate into the edge adhesive and reducelight scatter from propagating back through the eyepiece. For example,the edge adhesive may have an increasing concentration of carbon doping(such as carbon nanoparticles 50-70 nanometers in diameter) as the edgeis approached. Such a gradient may enable a progressive absorption oflight, reducing the light scattering off the adhesive with an abruptchange in refractive index compared to the interior of the eyepiece asmay occur with embodiments that attempt to absorb all light impactingit.

FIG. 7 illustrates one or more embodiments with progressively varyingconcentration of absorptive material (e.g., carbon). Although examplesherein describe the use of carbon as the absorptive material,embodiments may employ other suitable absorptive materials in variousconcentrations or arrangements. FIG. 7 depicts eyepiece 700 with anenlarged view of an edge portion 720 of the eyepiece 700. Eyepiece 700includes an eyepiece stack 702 comprising layers of optical components.Eyepiece stack 702 includes an outer edge 704 on which an edge material706 is disposed to seal outer edge 704 against outside contaminants, toprovide reinforcement to resist delamination of the optical layers,and/or to mitigate the reflection and/or scattering of stray light 710through the optical components. Edge material 706 may comprise multiplelayers 708 of materials as illustrated in FIG. 7, though fewer or morelayers are possible. Each layer may be the same material as one or moreof the other layers with a substantially similar index of refractionrelative to each other and eyepiece stack 702, or alternatively,different layers may be made of different materials. In someembodiments, at least one of the layers may comprise a doped materialmade up of one or more constituent materials, such as carbonnanoparticles. The ratio of the constituent materials may be differentfor each doped layer or may be substantially the same. In the embodimentshown in FIG. 7, four layers 708A, 708B, 708C, and 708D are disposedaround outer edge 704 of eyepiece stack 702 and are described hereinbelow.

In the embodiment illustrated by FIG. 7, first layer 708A may comprise amaterial, such as an epoxy, having a first index of refraction. Thefirst index of refraction of first layer 708A may be similar to orsubstantially the same as the index of refraction of eyepiece stack 702such that light 710 traveling toward outer edge 704 of eyepiece stack702 may pass through an interface between outer edge 704 of eyepiecestack 702 and edge material 706 into first layer 708A. Matching theindex of refraction between eyepiece stack 702 and first layer 708Aallows for light 710 to pass through the interface with minimalrefraction, reflection, and/or scatter of light back toward eyepiecestack 702. First layer 708A acts to receive a majority of light 710 fromeyepiece stack 702 into the edge material 706. In some embodiments,light 710 may then pass through first layer 708A toward second layer708B. In some embodiments, first layer 708A includes absorptive dopingmaterial in a desired concentration to absorb at least a portion oflight passing through it.

Second layer 708B may include a doped material. In the example shown inFIG. 7, second layer 708B may include a base material 714, such asepoxy, with particles 716 embedded in base material 714. Several designvariables may be adjusted to provide desired performance of layer 708Band edge material 706. For example, particle material, particle size,particle-to-base material ratio, and epoxy material are some of thedesign variables that may be adjusted for optimization.

In some embodiments, the embedded particles 716 may be light absorptiveparticles, such as carbon black nano-particles, and may be sized on theorder of nanometers. For example, embedded particles 716 may range insize from 50 to 70 nm. The ratio of embedded particles 716 to basematerial 714 may vary depending on desired performance of the layer. Forexample, a single layer, such as an adhesive tape applied to theexterior of eyepiece stack 702 may have a weight per weight (w/w) of 5%.In some embodiments, higher or lower ratios of embedded particles 716 tobase material 714 may also be used to optimize performance of edgematerial 706 across multiple layers. For example, second layer 708B mayhave a carbon nanoparticle w/w of 1%, and third layer 708C may have acarbon nanoparticle w/w of 3%.

Base material 714 of second layer 708B may be the same material as firstlayer 708A such that the index of refraction of second layer 708B issimilar to, or substantially the same as, the index of refraction oflayer 708A. The similarity between the two refraction indicesfacilitates light 710 entering second layer 708B from first layer 708Awith minimal refraction or reflection.

The composition of embedded particles 716 disposed within base material714 in second layer 708B allows a portion of light 710 to be absorbed bysecond layer 708B. For example, light 710 traveling into second layer708B may encounter one or more embedded particles 716 where it isabsorbed. Light 710 that does not encounter an embedded particle 716 maycontinue to travel through base material 714 of second layer 708B towardthird layer 708C.

Third layer 708C may be a doped material having embedded particles 716disposed within a base material 714. The base material 714 of thirdlayer 708C may be selected to have the same or similar index ofrefraction as the base material of second layer 708B. Having a same orsimilar index of refraction between the layers facilitates light 710crossing through the interface between second and third layers 708B,708C, respectively. In some embodiments, the base material 714 of thirdlayer 708C may be the same material as the base material of second layer708B, such as an epoxy material. In the embodiment shown in FIG. 7,third layer 708C further includes embedded particles 716. The ratio ofembedded particles to base material may be substantially the same asanother layer, or alternatively, may have a different ratio. In theexample shown, third layer 708C may have a higher ratio of embeddedparticles to base material as compared with second layer 708B. Similarto second layer 708B, light entering third layer 708C may encounterembedded particles 716 which absorb the light. Light 710 that does notencounter an embedded particle continues through base material 714toward fourth layer 708D. It is possible that at least a portion oflight 710 that transmits through second layer 708B will reflect orscatter upon the interface between second layer 708B and third layer708C. Embedded particles 716 in second layer 708B may then furtherabsorb such reflected or scattered light.

Fourth layer 708D may be a doped material similar to third layer 708Chaving a base material 714 with embedded particles 716. The basematerial of fourth layer 708D may be selected to have an index ofrefraction similar to the base material of third layer 708C tofacilitate light entering fourth layer 708D from third layer 708C. Incertain embodiments, base material of fourth layer 708D may be the sameas base material of third layer 708C, such as an epoxy material.Embedded particles 716 may be light absorptive particles, and may bemade of a carbon black material. The ratio of embedded particles to basematerial may be substantially the same as another layer, or may have adifferent ratio. As shown in FIG. 7, fourth layer 708D may have a higherratio of embedded particles to base material as compared with secondlayer 708B or third layer 708C. Light entering fourth layer 708D mayencounter and be absorbed by embedded particles 716. Light that does notencounter an embedded particle may continue to travel through basematerial 714. It is possible that at least a portion of light 710 thattransmits through third layer 708C will reflect or scatter upon theinterface between third layer 708C and fourth layer 708D; embeddedparticles 716 in third layer 708C may then further absorb such reflectedor scattered light.

After passing through all of the layers of edge material 706, verylittle light will remain unabsorbed. However, light 710 that does reachan outermost edge 718 of edge material 706 may be reflected back intofourth layer 708D. This light may continue to pass through the multiplelayers 708D, 708C, 708B where it will have additional absorption eventsby the embedded particles 716 of the respective multiple layers.

One of skill in the art will appreciate that many variables may bealtered within the scope of the present disclosure. For example, thenumber and composition of layers may be adjusted to provide more or lesslight absorption, reflection, and refraction. In addition, the thicknessof each layer may be varied. As discussed above, the base material andembedded particles may be epoxy and carbon black particles,respectively; however, other glues, adhesives, and known sealingmaterials may be used as the base, and other types and sizes ofparticles may also be used in addition to or in place of the carbonblack particles disclosed. These design changes may be used to optimizethe edge material configuration to improve light absorption, cost,aesthetic appeal, ease of manufacture, weight, durability, or any otherselected variable.

The edge material disclosed may be manufactured by dropping dots of eachlayer material around the edge of the eyepiece stack and curing onelayer at a time to form as many layers as desired. With each layer, thematerial composition, in particular the embedded particle-to-basematerial ratio, may be changed to create the seal described above.Alternatively, edges of the eyepiece stack may be dipped into the layermaterial and cured, then dipped into material for the adjacent layer andcured, and so on until the desired layer build up is finished.

In yet another alternative embodiment, each layer may be pre-formed asan adhesive tape that may be wrapped around the edge of the eyepiecestack. For example, referring to the edge material shown in FIG. 7, fourdifferent tapes can be used. The first tape wrapped directly aroundouter edge 704 of eyepiece stack 702 would comprise first layer 708A.This tape may be made up of a uniform epoxy material. To form secondlayer 708B, a section of tape made up of epoxy and a selectedconcentration of carbon particles may be wrapped over first layer 708A.Third and fourth layers 708C and 708D would be sequentially wrappedaround the previous layer to build up the final thickness of edgematerial 706. In some embodiments, the multiple layers of tape may bestacked prior to wrapping the tape around the eyepiece 700 so that fewerwrapping steps are performed.

In some embodiments, the grating structures to control wicking maycontrol the gradient concentration of embedded particles 716. Forexample, in a wicking gradient pattern with a pitch, or space betweengratings, pillars, or relief structures otherwise, or 400-600 nm nearthe outside edge of the eyepiece stack, but become gradually narrower tohave a pitch of 100 nm approaching the functional area of the eyepiece.In such an embodiment, the adhesive doped with carbon material wouldwick into the larger pitch more easily than into the smaller pitch, thusintroducing fewer carbon particles into the adhesive closer to thefunctional area as compared to the adhesive nearer the outside edge. Thesize of the carbon nanoparticles could further control the concentrationof embedded particles in such embodiments; by having carbonnanoparticles greater than 100 nm, or carbon nanoparticles of varyingdimensions doped into a common adhesive or epoxy, only certain sizeswould wick into certain portions of the structures. In such embodiments,a common percentage w/w but a variable carbon particle size couldproduce a gradient in the carbon distribution across the layers.

FIG. 8 illustrates an example of a gradient carbon blacking by suchvariable pitch. FIG. 8 depicts an example eyepiece 800, with an enlargedview 804 of an edge portion 802 of the eyepiece 800. As depicted in FIG.8, grating structure 820 is closer to a functional area of an eyepiecerelative to grating structure 825. Grating structure 825 has a widerpitch 815, as compared to narrower pitch 810 between grating structure820. As a result, carbon doped adhesive or sealant entering the gratingpattern will move more easily through pitch area 815 than pitch area810, and given a carbon nanoparticle size embedded, more carbonparticles will occupy pitch area 815 than pitch area 810 to provide agradient absorption profile as a function of grating pattern. In suchembodiments, even a constant density of carbon particles throughout theadhesive will yield a gradient absorption profile due to the varyingamount of adhesive across the profile that may occupy the space betweenthe gratings 815 or 825. In some embodiments, the sealant (e.g., edgematerial 108) may have a refractive index that is the same, orsubstantially the same, as the refractive index of the material of theeyepiece (e.g. the refractive index of the substrate of the variouslayers of the eyepiece structure). In some embodiments, the sealant mayhave a variable density through its cross section, such that the sealantis denser at the surface that is opposite to the direct interface and/orapplication to the eyepiece, and less dense nearer to its interface withthe eyepiece.

In some embodiments, and as depicted in FIG. 9, a combination of edgeblackening and a separate adhesive is applied. In such an embodiment, ablackening layer may be first applied to wick into the edge patternsfirst, and then a second adhesive material applied to bind the layerstogether. Such a combination permits maximizing the reflectionmitigation of the blackening material without potential tradeoffs toenhance adhesion, and similarly maximizes the properties of theadhesive. FIG. 9 depicts a cross-sectional view of an example eyepiece200, including a combination of light mitigation material 902 andadhesive material 904, according to some embodiments of the presentdisclosure. As shown FIG. 9, in some embodiments an adhesive material904 may be used to bind the layers of substrate 104 to one another inthe eyepiece 200, and a separate, different edge material 902 may beused for light mitigation. As shown, the edge material 902 may be ablackening material applied to the edge region of the various layers, toabsorb light that reaches the edges. In some embodiments, the adhesivematerial 904 has a same (or substantially similar) refractive index asthat of the substrate 104.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of the disclosure or of what maybe claimed, but rather as descriptions of features specific toparticular embodiments. Certain features that are described in thisspecification in the context of separate embodiments may also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment mayalso be implemented in multiple embodiments separately or in anysuitable sub-combination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination may in someexamples be excised from the combination, and the claimed combinationmay be directed to a sub-combination or variation of a sub-combination.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the disclosure. For example, various structuresshown above may be used, with elements rearranged, positioneddifferently, oriented differently, added, and/or removed. Accordingly,other embodiments are within the scope of the following claims.

What is claimed is:
 1. An optical structure comprising: a substrateincluding an edge grating pattern that is proximal to an edge of thesubstrate, the edge grating pattern including one or more featuresarranged to control capillary flow of a material from the edge of thesubstrate into the edge grating pattern.
 2. The optical structure ofclaim 1, wherein: the edge grating pattern is on a first surface of thesubstrate; and the substrate further includes a second grating patternon a second surface of the substrate.
 3. The optical structure of claim2, wherein the second grating pattern is a functional grating patternthat includes one or more of an orthogonal pupil expander (OPE) regionand an exit pupil expander (EPE) region.
 4. The optical structure ofclaim 1, wherein the one or more features are arranged to besubstantially perpendicular to the edge of the substrate.
 5. The opticalstructure of claim 1, wherein the one or more features include one ormore of a V-shaped grating pattern, an S-shaped grating pattern, and arectangular grating pattern.
 6. The optical structure of claim 1,wherein the edge grating pattern further includes one or more secondfeatures arranged to inhibit the capillary flow of the material beyondthe edge grating pattern.
 7. The optical structure of claim 6, whereinthe one or more second features are arranged to be substantiallyparallel to the edge of the substrate.
 8. The optical structure of claim6, wherein the one or more second features differ, at least in part,from the one or more features in at least one of depth, height, andwidth.
 9. The optical structure of claim 1, wherein the material has arefractive index that is lower than that of the substrate.
 10. Theoptical structure of claim 1, wherein the material, as applied, has agradient of refractive index that varies according to a distance fromthe edge of the substrate.
 11. The optical structure of claim 1, whereinthe one or more features have a cross-sectional shape of at least onepolygon.
 12. The optical structure of claim 11, wherein the at least onepolygon includes one or more of a triangle, a square, and a rectangle.13. The optical structure of claim 1, wherein: the substrate is awaveguide configured to receive and propagate light; and the material isa light variable absorptive edge material configured to receive andabsorb light from the waveguide.
 14. The optical structure of claim 1,wherein the material and the substrate have a substantially same indexof refraction.
 15. The optical structure of claim 1, wherein thematerial comprises a doping agent and an adhesive.
 16. The opticalstructure of claim 15, wherein the doping agent is distributed at agradient that varies with distance from an edge of the waveguide. 17.The optical structure of claim 15, wherein the doping agent comprisescarbon black nanoparticles.
 18. The optical structure of claim 17,wherein the carbon black nanoparticles have a diameter in a range of50-70 nm.
 19. The optical structure of claim 1, wherein the materialcomprises at least one layer of adhesive tape.
 20. The optical structureof claim 19, wherein the adhesive tape comprises a doping agent and anadhesive.
 21. The optical structure of claim 19, wherein the adhesivetape and the substrate have a substantially same index of refraction.22. The optical structure of claim 1, wherein: the substrate is one of aplurality of layers of substrate included in the optical structure; eachof the plurality of layers includes the edge grating pattern proximal toa respective edge of the layer; and the material is an edge adhesivethat is applied along at least a portion of a perimeter of the opticalstructure to secure the plurality of layers of substrate.
 23. Theoptical structure of claim 22, wherein each of the plurality of layersof substrate further includes a second grating pattern.
 24. The opticalstructure of claim 23, wherein the edge grating pattern is arranged toprovide for a capillary flow of the edge adhesive into the edge gratingpattern, and is further arranged to inhibit the capillary flow of theedge adhesive into the second grating pattern.
 25. The optical structureof claim 23, wherein: the second grating pattern is of a nano-scale andoperate as a waveguide for light propagation; and the edge gratingpattern is one or more of a micro-scale and a nano-scale.